Silane

Silanes - rocket propellant characteristics

 

The data that is available on this website provides you with thermodynamic data for various silanes up to the pentasilanes ready to be used to conduct computations with the NASA CEA2 program as well as with the well-known CHEMKIN program. The way the thermodynamic data is stored in both programs' databases differs slightly: while the NASA CEA2 program uses 7th order polynomials for the thermodynamic functions, the CHEMKIN program uses only 5th order polynomials. For details on the data set entry structure please refer to the programs' manuals.

 

Both my diploma thesis (German only, PDF, 4.4 MB) carried out at the University of the Armed Forces, Munich, Germany, and the ESA ITI 18691 Project (on-going activity) aim at the investigation of the possibility of using various silanes as rocket propellants. Amongst a lot of other requirements, a rocket propellant fuel should contain a lot of inner energy, and release a lot of energy during combustion with the oxidant while forming new chemical compounds. One main advantage of the silanes is their strong endothermic character. Silanes have positive heats of formation, which means that thermic decomposition of silanes releases energy. Thus, silanes could be used as monopropellants just like hydrazine. Alkanes, on the other hand, are exothermic substances. Therefore, the heats of formation of silanes and alkanes are diametrally opposed. The liquid temperature interval of the silanes is shifted to higher temperatures when compared to the alkanes due to their higher molecular masses and densities. For the same reason, the viscosities of the silanes are higher than those of the alkanes. Little data is available in literature concerning the heats of vaporization.

 

The following links contain the thermodynamic data sets for the silanes. They were calculated by the THERMO computer program written by Gernot Katzer and made usable for CHEMKIN and CEA2 by using the NASA program PAC99. For some of the lower silanes, the CHEMKIN and CEA2 databases already contained data. In these cases, the original database entries are printed too. With these data, chemical equilibrium calculations as well as calculations of rocket performance characteristics such as the specific impulse were conducted by means of CHEMKIN and CEA2. The chemical equilibrium compositions were cross-checked by both programs and show no significant aberration. Here are some of the resulting adiabatic flame temperatures and chemical equilibrium compositions in the combustion chamber at 70 bar (hp-problem):

 

Next, CEA2 was applied to calculate specific impulses at the nozzle end assuming shifting equilibrium. Again, the oxidator LOX was used and the chamber pressure was 70 bar.

 

 

The following two postscript files show the specific impulses and the adiabatic flame temperatures of the linear silanes in one graph. The specific impulses decrease with increasing chain length due to the gradual reduction of the hydrogen fraction in the sum formula.

 

 

 


 

Notes

Please adress all comments or questions to Bernhard Hidding (hidding@uni-duesseldorf.de).
This website was last updated on 2005/06/01.